Semiconductor chips typically are connected to external circuitry through contacts on a surface of the chip. The contacts on the chip typically are disposed in the regular patterns such as a grid substantially covering the front surface of the chip, commonly referred to as an "area array" or in elongated rows extending parallel to and adjacent each edge of the chip front surface. Each contact on the chip must be connected to external circuitry, such as the circuitry of a supporting substrate or circuit panel. Various processes for making these interconnections use prefabricated arrays of leads or discrete wires.
The rapid evolution of a semiconductor art in recent years has created a continued demand for progressively greater numbers of contacts and leads in a given amount of space. An individual chip may require hundreds or even thousands of contacts, all within the area of the chip front surface. For example, a complex semiconductor chip in current practice may have a row of contacts spaced apart from one another at center-to-center distances of 0.5 mm or less and, in some cases, 0.1 mm or less. These distances are expected to decrease progressively with continued progress in the art of semiconductor fabrication.
With such closely-spaced contacts, the leads connected to the chip contacts must be extremely fine structures, typically less than 0.5 mm wide. Such fine structures are susceptible to damage and deformation. With closely spaced contacts, even minor deviation of a lead from its normal position will result in misalignment of the leads and contacts. Thus, a given lead may be out of alignment with the proper contact on the chip or substrate, or else it may be erroneously aligned with an adjacent contact. Either condition will yield a defective chip assembly. Errors of this nature materially reduce the yield of good devices and introduce defects into the product stream. These problems are particularly acute with those chips having relatively fine contact spacings and small distances between adjacent contacts.
Certain connection systems described in U.S. Pat. Nos. 5,148,265 and 5,148,266 include an interposer or connection component incorporating dielectric layers with arrays of prefabricated leads. The leads are connected to the chip thereby connecting terminals on the component to the chip. These terminals are then connected to an external circuit.
Copending, commonly assigned U.S. patent application Ser. No. 07/919,772, filed Jul. 24, 1992, now U.S. Pat. No. 5,360,947 the disclosure of which is incorporated by reference herein, also describes an improved system for connecting semiconductor chips to external circuitry. Certain embodiments of the invention set forth in the '772 application utilize a connection component having a support structure and electrically conductive leads. Each lead has an elongated connection section extending across a gap in the support structure. The connection sections of the leads are flexible. Preferably, one end of each connection section is detachably secured to the support structure, whereas the other end is permanently secured to the support structure and connected to a terminal mounted on the support structure. The connection component is positioned on a part of a semiconductor chip assembly, such as on the chip itself, so that the leads overlie contacts on the part or chip. The connection sections of the leads are bonded to the contacts on the chip by engaging each connection section with a tool, forcing the tool downwardly to break the detachable end of the lead from the support structure and bring the connection section into engagement with a contact on the chip. The tool is used to apply heat, pressure and/or vibrations to the lead, thereby forming a bond between the lead and the contact of the chip. This process is repeated for each lead, until all the leads have been bonded to the contacts on the chip. After the connection component has been electrically connected to the contacts of the chip, the terminals of the connection component can be used to connect the chip to other, external circuitry as, for example, by bonding the terminals of the connection component to an external substrate such as a circuit panel.
In the preferred arrangements disclosed in the '772 application, the bonding tool is arranged to capture and align the lead. Thus, the bonding tool may be a blade-like device with an elongated bottom edge and with a groove extending lengthwise along such bottom edge for engaging leads to be bonded. The groove may have a central plane and surfaces sloping upwardly from the sides of the groove towards the central plane. When the tool is roughly aligned with a lead, so that the lengthwise axis of the bottom edge and groove are generally parallel to the lengthwise axis of the connection section of the lead, the groove will engage the lead and guide it into precise alignment with the tool. Thus, the tool can be aligned in sequence with each contact, and engaged with a lead. Even if the lead is slightly out of alignment with the contact and tool at the beginning of the operation, the tool will bring the lead into precise alignment with the tool and hence with the contact during the downward motion of the tool. Thus, minor dimensional variations in the connection component do not impede the process, even where the contacts are provided at very small spacings.
The copending, commonly assigned U.S. patent application Ser. No. 08/096,700 of Thomas DiStefano et al. entitled SEMICONDUCTOR INNER LEAD BONDING TOOL, filed of even date herewith, the disclosure of which is incorporated by reference herein, discloses a tool for bonding leads to contacts on parts such as semiconductor chips, which tool can operate on leads extending in either of two orthogonal directions. Such a tool is referred to herein as a "bidirectional" tool. A bidirectional tool has a body with a lower end surface including a bonding surface region. The lower end of the tool may define guide surfaces for engaging elongated leads disposed beneath the lower end of the tool upon downward movement of the tool from above the leads. The guide surfaces are adapted to engage an elongated lead extending generally in a first horizontal direction beneath the lower end and to guide any such lead generally in a second horizontal direction orthogonal to the first direction so as to align the lead with the bonding region of the lower end. The guide surfaces are also adapted to engage an elongated lead extending generally in the second horizontal direction beneath the lower end and to guide the lead generally in the first horizontal direction so as to align such a lead with the bonding region. Stated another way, the guide surfaces are adapted to engage a lead extending in either of two mutually orthogonal directions and to center the engaged lead beneath the bonding region of the lower end so that the lead can be engaged and bonded by the tool.
A tool of this nature will operate on leads extending in either of two mutually orthogonal directions relative to the tool. With either orientation of the lead, the tool will capture and align the lead, and bring the lead into position for bonding. Such a tool can be used in procedures generally similar to those discussed above with reference to the '772 application. Use of a bidirectional tool simplifies the process in that there is no need to rotate the tool relative to the parts.